The aim of log mode COW is solve extent tree performance issue when free metadata space are scarce and fragmented. The basic idea is: when cowing a non-shared block, we insert a log entry that maps the new block to the old block into a special log tree, and do not update the extent tree. After transaction is fully committed, copy the new block back to the old location. Log mode COW can be enabled/disabled by log_mode=%d mount option. ''0'' means disable log mode COW; ''1'' means enable log for tree blocks that are not reference counted; ''2'' means enable log for all tree blocks are not shared. NOTE: The patch series base on current btrfs-unstable. They are for test and review only. Enable log mode COW changes disk format. Regards Yan, Zheng -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html